enzymes are a class of proteins that catalyze the conversion of a substrate from one form to another without themselves being destroyed. Almost all metabolic processes and reactions within living cells are mediated by enzymes. A typical cell has several thousand kinds of enzymes that carry out its functions. One of the most important features of an enzyme is its active site, where a cluster of amino acids is folded together to create a pocket or a groove where the catalytic event occurs. This pocket is very specific and selective. Researchers often suggest a lock-and-key analogy with enzymes. Recent evidence, however, suggests the effect is more like a baseball glove: the glove is the enzyme that folds around the substrate. Because of this precise attraction of an active site to a substrate, enzymes are highly effective at binding and creating very fast reactions, much more so than an inorganic catalyst like a metal ion. Initial contact between an active site and a potential substrate is a random collision. The two are held together by hydrogen or ionic bonds to amino acids that carry a mild charge. Protons and electrons (energy) will be either donated or accepted between enzyme and substrate. In response, the substrate is either broken apart or joined with another substrate. The enzyme then detaches and repeats the process.
Because they can be sensitive to external pressures, the environment in which enzymes conduct their activities is important. Scientists devote careers to the study of optimizing enzyme performance, known as enzyme kinetics. The two most important parameters of enzyme activity they study are temperature and pH. See pH. Temperature increases within limits often increase reaction rates between enzymes and substrates. As biological material, however, enzymes will denature when exposed to sufficiently high temperatures. Enzymes are unique, and each will deactivate at its own specific temperature. Enzymes that can function at higher temperatures are called thermotolerant. Likewise, the pH of the surrounding environment can affect the ionic charges either on the substrate or on the enzyme, thus affecting the binding process. A third factor enzyme scientists consider is the concentration of either enzyme or substrate. Increasing the concentration of enzyme to substrate will increase the reaction rate, but the effect is not linear. When the enzyme concentrate becomes saturated, reaction rates only marginally improve.
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By: Don Livermore